Transfer conveyors have already been proposed which include conveyor chains which circulate endlessly about reversing pulleys transversely to the conveying direction of at least the first piece goods conveyor and beneath the conveying plane thereof and which chains are provided with lifting elements which are situated beneath the conveying plane of said first piece goods conveyor in a pass-through position and in a transfer position project simultaneously above said conveying plane at a predefined distance from each other which is less than the width of the piece goods.
German Offenlegungsschrift 2,259,273 discloses a system of this kind in which the conveyor chains with lifting elements are guided in the region of the conveyor plane over guide rails on which cam tracks are formed on which the lifting elements are guided upwardly by means of a rising ramp and from which the lifting elements are guided downwardly by means of a falling ramp. Lifting elements situated on opposite sides of a conveyor chain are disposed at a defined distance from each other which is shorter than the width of the piece goods which are to be transferred. Each lifting element is associated with its own cam track and the rising and falling ramps of two adjacent cam tracks must be offset relative to each other at the same defined distance. The known device suffers from the disadvantage of calling for guide rails which have to be constructed with cam tracks as well as rising and falling ramps. Moreover, resilient chain tensioning means must be provided for each conveyor chain because the circumference of the chain is deformed in the course of its movement when the lifting elements move via the rising ramps on to the cam tracks and again slide off the cam tracks via the falling ramps.
The prior art also discloses a system (U.S. Pat. No. 3,104,004) in which a circulating chain is provided which is inclined at an angle to the horizontal and in which drivers are secured on one chain member, one behind the other, the vertical extent of which said drivers increases from the front to the rear in the direction of movement so that all drivers project simultaneously above the plane of the piece goods conveyor to lift one item of piece goods.
The construction and installation of these known systems is very complex owing to the drivers of varying size required for such a system. Moreover, the known system is unsuitable for transferring two conveyors which are disposed parallel with each other because the transfer system itself can deposit an item of piece goods on to a second piece goods conveyor extending transversely to the transfer direction only by the use of great force, once such an item of piece goods has been lifted, because in this case the group of drivers must first be withdrawn from beneath the item of piece goods which is retained by a stop abutment while the item of piece goods itself is raised.
The prior art discloses a system (German Offenlegungsschrift 2,515,024) in which the lifting elements are hinged to the conveyor chains in the form of pivoting levers.